The present invention relates generally to a printing apparatus. More particularly, the present invention relates to a printing apparatus having a technical concept employed therefor for detecting a malfunction that the printing apparatus is clogged with part of a band-shaped copying paper for which a recording operation can be performed.
A conventional printing apparatus of the type including detecting means for detecting a malfunction that the printing apparatus is clogged with a fraction of printing paper is hitherto known as disclosed in an Unexamined Japanese Patent Publication (Kokai) No. Sho. 51-78245. The detecting means disclosed in the official gazette of the prior invention will be described below with reference to FIG. 13.
In the drawing, reference numeral 8 designates a printing medium such as a sheet of printing paper or the like. The printing medium 8 is conveyed further while it is held between a plurality of driving rollers 11 and a plurality of clamping rollers 10a in the clamped state. The contact rollers 10a are normally biased toward the driving rollers 11 so that they are followably rotated by the printing medium 8 while they are brought in contact with the printing medium 8. A circular rotary plate 10b is fixedly secured to the right-hand end of a shaft for the contact rollers 10a such that it is rotated together with the contact rollers 10a. The circular rotary plate 10b serves as an encoder including two magnets 23 along the outer periphery thereof. With this construction, a conveying speed of the printing medium 8 is detected in the form of an electrical signal as a lead switch 21 is turned on or off by the magnets 23.
The conventional printing apparatus is equipped with two paper speed detecting mechanism each constructed in the above-described manner along a paper conveyance path in order to detect a malfunction that the printing apparatus is clogged with a part of the recording medium 8 based on the difference arising between the conveying speed of the recording medium 8 detected by the first paper speed detecting mechanism and the conveying speed of the same detected by the second paper speed detecting mechanism.
According to the aforementioned technical concept, since the contact rollers 10a and the circular rotary plate 10b are rotated by bringing the contact rollers 10a in contact with the printing medium 8, a certain magnitude of rotational load appearing attributable to the arrangement of the contact rollers 10a, the circular rotary plate 10b and the shaft extending through the contact rollers 10a and the circular rotary plate 10b is applied to the contact surface of the printing medium 8. This rotational load functions as a shearing power effective in the conveying direction of the recording medium 8.
In the case that the recording medium 8 is prepared in the form of a band-shaped copying paper having plural sheets of papers laminated one above another, positional offsetting is unavoidably caused between the paper coming in contact with the driving rollers 11 and the paper coming in contact with the contact rollers 10a. As a result of the foregoing positional offsetting, there arises a problem that the printed positions on the respective papers laminated in that way are slightly deviated away from each other.
In addition, as shown in FIG. 14, since a folded part or a glueing part 8a on the band-shaped copying paper 8 collides against the contact rollers 10a as the driving rollers 11 are rotated, the rotational load to be applied to the band-shaped copying paper 8 from the contact rollers 10a increases. Due to the increased rotational load, there arises another problem that slippage occurs between the driving rollers 11 and the band-shaped copying paper 8, resulting in the driving torque given by the driving rollers 11 failing to be transmitted to the band-shaped copying paper 8. This leads to the result that the printing apparatus is undesirably clogged with a part of the band-shaped copying paper 8. In other words, the detecting mechanism for detecting a malfunction of paper clogging disadvantageously serves to induce a malfunction that the printing apparatus is clogged with a fraction of paper.